Method for transmitting D2D synchronization signal and terminal therefor

Abstract

Disclosed is a method for transmitting a synchronization signal of device-to-device (D2D) communication. The method for transmitting a D2D synchronization signal of the present application may comprise a step for transmitting a D2D synchronization signal according to one of transmission modes predetermined on the basis of an instruction of a base station. In addition, a transmission mode for D2D transmission may comprise a transmission mode on the basis of a signaling from the base station and a transmission mode on the basis of a reference signal reception power.

What is claimed is: 
     
       1. A method for transmitting a device-to-device (D2D) synchronization signal by a user equipment (UE) in a wireless communication system, the method comprising:
 receiving, from a base station, a first signal used for a D2D synchronization signal transmission mode including a first transmission mode and a second transmission mode; and 
 performing transmission of the D2D synchronization signal based on the first or the second transmission mode based on the first signal, 
 wherein, in the first transmission mode, the transmission of the D2D synchronization signal is performed based on a signal from the base station, which is used for initiation of the D2D synchronization signal transmission, 
 wherein, in the second transmission mode, the transmission of the D2D synchronization signal is performed when a reference signal received power (RSRP) is equal to or smaller than a predetermined first threshold value, 
 wherein, despite the RSRP exceeding the first threshold value in the second transmission mode, a modification of the second transmission mode to the first transmission mode is performed when a modification signal is received, and 
 wherein the modification signal is used for the modification of the second transmission mode to the first transmission mode. 
 
     
     
       2. The method of  claim 1 , wherein the first signal is received through a predetermined dedicated signal, a predetermined radio resource control (RRC) signaling, or a system information block (SIB). 
     
     
       3. The method of  claim 1 , wherein the first signal is a UE-specific signal, a UE-group-specific signal, or a cell-specific signal. 
     
     
       4. The method of  claim 1 , wherein when the UE is out of coverage of the base station and a RSRP of a predetermined second signal from the base station is equal to or smaller than a predetermined second threshold value, the D2D synchronization signal is transmitted on a predetermined D2D synchronization signal resource as a D2D synchronization source. 
     
     
       5. The method of  claim 4 , wherein transmitting the D2D synchronization signal as the D2D synchronization source is performed independently of scheduling assignment and D2D data of the UE. 
     
     
       6. The method of  claim 4 , wherein transmitting the D2D synchronization signal as the D2D synchronization source comprises periodically transmitting the D2D synchronization signal at a predetermined period. 
     
     
       7. The method of  claim 4 , wherein the predetermined second signal comprises at least one of a demodulation-reference signal (DM-RS), a primary D2D synchronization signal (PD2DSS), a secondary D2D synchronization signal (SD2DSS), or a physical D2D shared channel (PD2DSCH). 
     
     
       8. A user equipment (UE) for transmitting a device-to-device (D2D) synchronization signal, the UE comprising:
 a transceiver configured to transmit and receive radio signals; and 
 a processor for controlling the transceiver, 
 wherein the processor is configured to:
 receive, from a base station, a first signal used for a D2D synchronization signal transmission mode including a first transmission mode and a second transmission mode; and 
 perform transmission of the D2D synchronization signal based on the first or the second transmission mode based on the first signal, 
 wherein, in the first transmission mode, the transmission of the D2D synchronization signal is performed based on a signal from the base station, which is used for initiation of the D2D synchronization signal transmission, 
 wherein, in the second transmission mode, the transmission of the D2D synchronization signal is performed when a reference signal received power (RSRP) is equal to or smaller than a predetermined first threshold value, 
 wherein, despite the RSRP exceeding the first threshold value in the second transmission mode, a modification of the second transmission mode to the first transmission mode is performed when a modification signal is received, and 
 wherein the modification signal is used for the modification of the second transmission mode to the first transmission mode. 
 
 
     
     
       9. The UE of  claim 8 , wherein the first signal is received through a predetermined dedicated signal, a predetermined radio resource control (RRC) signaling, or a system information block (SIB). 
     
     
       10. The UE of  claim 8 , wherein the first signal is a UE-specific signal, a UE-group-specific signal, or a cell-specific signal. 
     
     
       11. The UE of  claim 8 , wherein when the UE is out of coverage of the base station and a RSRP of a predetermined second signal from the base station is equal to or smaller than a predetermined second threshold value, the D2D synchronization signal is transmitted on a predetermined D2D synchronization signal resource as a D2D synchronization source. 
     
     
       12. The UE of  claim 11 , wherein the processor is further configured to transmit the D2D synchronization signal as the D2D synchronization source, independently of scheduling assignment and D2D data of the UE. 
     
     
       13. The UE of  claim 8 , wherein the predetermined second signal comprises at least one of a demodulation-reference signal (DM-RS), a primary D2D synchronization signal (PD2DSS), a secondary D2D synchronization signal (SD2DSS), or a physical D2D shared channel (PD2DSCH).